This invention relates generally to inkjet printers. More specifically, the present invention relates to selective drop detection of printhead nozzles corresponding to the effect of the ink on print media fired from those nozzles.
Inkjet printing mechanisms, e.g., printers, photocopiers, facsimile machines, etc., typically implement inkjet cartridges, often called xe2x80x9cpensxe2x80x9d to shoot drops of ink onto a sheet of print media, e.g., paper, fabric, textile, and the like. Some inkjet printing mechanisms carry an ink cartridge with an entire supply of the ink back-and-forth across the sheet. Other inkjet print mechanisms, known as xe2x80x9coff-axisxe2x80x9d systems, propel only a relatively small ink supply with the printhead carriage across the print zone, and store the main ink supply in a stationary reservoir, located off-axis from the path of the printhead travel. Typically, a flexible conduit or tubing is used to convey the ink from the off-axis reservoir to the printhead cartridge.
Pens typically have a printhead that includes very small nozzles on an orifice plate through which the ink drops are fired. The particular ink ejection mechanism within the printhead may take on a variety of different forms as known to those skilled in the art, such as those using piezoelectric or thermal inkjet technology. To print an image, the printhead is scanned back-and-forth across a print zone above the sheet, with the pen shooting drops of ink as it moves. By selectively firing ink through the nozzles of the printhead, the ink is expelled in a pattern on the print media to form a desired image (e.g., picture, chart, text and the like). The nozzles are typically arranged in one or more linear arrays along the printhead. If more than one, the two linear arrays are typically located side-by-side on the printhead, parallel to one another, and substantially perpendicular to the scanning direction. Thus, the length of the nozzle arrays defines a print swath or band. That is, if all the nozzles of one array were continually fired as the print head made one complete traverse through the print zone, a band or swath of the ink would appear on the sheet. The height of this band is known as the xe2x80x9cswath heightxe2x80x9d of the pen, the maximum pattern of ink which can be laid down in a single pass.
The orifice plate of the printhead has a tendency to pick up contaminants, such as paper dust, and the like, during the printing process. Such contaminants may adhere to the orifice plate either because of the presence of ink on the printhead, or because of electrostatic charges. In addition, excess dried ink can accumulate around the printhead. The accumulation of either ink or other contaminants can impair the quality of the output by interfering with the proper application of ink to the print media. In addition, if color pens are used, each printhead may have different nozzles which each expel different colors. If ink accumulates on the orifice plate, mixing of different colored inks (cross-contamination) can result during use which may lead to adverse affects on the quality of the resulting printed product. Furthermore, the nozzles may become clogged, particularly if the printheads are left uncapped for a relatively long period of time. For at least these reasons, it is desirable to clear the printhead orifice plate of such contaminants on a substantially routine basis.
In this respect, servicing operations, including ink drop detections, are typically performed on the nozzles prior to, during, and/or after completion of the performance of a printing operation. In performing the servicing operations, inkjet printing mechanisms typically implement a service station located along the scanning direction. The service station typically performs a plurality of servicing operations on the nozzles, e.g., collecting spit ink, capping the nozzles, wiping the orifice plate, etc.
The manner and form of the servicing operations are typically controlled by a servicing protocol that uses a drop detector to determine whether any of the nozzles are operating in an improper manner, e.g., nozzle outs, paper crashes, and the like. As an example, a servicing operation may be triggered when the drop detector determines that a nozzle in a printhead is clogged or otherwise improperly ejecting ink. The servicing protocol may control the printheads of a printer mechanism to travel over the drop detector at certain times before, during and after performance of a printing operation. Typically, once the printheads are maneuvered over the drop detector, each of the nozzles contained in each of the printheads is tested. Although this type of complete nozzle testing is typically beneficial to the quality of the printed output, the amount of time required to perform the ink drop detections on all of the nozzles (e.g., known inkjet printing mechanisms may include six or more printheads, each of which may include two rows of 524 nozzles) typically negatively impacts throughput, i.e., amount of time required to print a plot, especially with regard to servicing operations performed during the printing process.
According to an aspect, the present invention pertains to a method of selective servicing operation performance. In the method, a degree of impact ink drops configured to be fired from each of a plurality of printheads has on a printed output is determined. Each of the printheads is characterized into at least one of a plurality of groups based upon the degree of impact of the ink drops. In addition, a selective servicing operation is performed on a first printhead group configured to fire ink drops having a predetermined degree of impact on the printed output.
According to another aspect, the present invention relates to an apparatus for operating a printing mechanism having a plurality of printheads, each printhead being configured to fire ink drops having various degrees of impact on a printed output. The apparatus includes a controller operable to control the plurality of printheads to fire ink drops onto a print medium to form the printed output. The controller also includes a memory configured to store the varying degrees of impact of the ink drops configured to be fired through the printheads. The controller is further operable to group the printheads according to the degrees of impact of each ink configured to be fired therefrom. The controller is operable to a control at least one of the printhead groups to undergo a selective servicing operation performance. The at least one of the printhead groups are those printheads configured to fire ink drops having a predetermined degree of impact on the printed output.
In comparison to known printing mechanisms and techniques, certain embodiments of the invention are capable of achieving certain advantages, including some or all of the following: (1) time savings in performance of servicing operations; (2) ink savings during the performance of ink drop detections; (3) substantial optimization of the servicing operation process; (4) substantial conformance of the servicing operation performances based upon user preferences. Those skilled in the art will appreciate these and other advantages and benefits of various embodiments of the invention upon reading the following detailed description of a preferred embodiment with reference to the below-listed drawings.